Formed politically by the anti-Vietnam war movement, he joined the Labour Party in 1969 and was active on the Labour left in Leeds from the late 1960s. From 1974 to 1986 he worked as a builder and plumber. During the campaigns relating to the Common Market referendum in 1975 he was the secretary of the Vote No campaign in Leeds.

During the 1970s Trickett was a member of the ILP (the successor body of the Independent Labour Party), contributed to its newspaper, the Labour Leader, and was elected for a number of years to its ruling body, the National Administrative Council. Trickett was also active in anti-fascist and anti-war movements, and was a delegate to the Leeds Trades Council. Later he was the election agent for Michael McGowan who became the MEP for Leeds in 1984.

Trickett was first elected to Leeds City Council for the Beeston ward in 1984 at the age of 34. He became Leader of the Council in 1989, holding the leadership until 1996 and his election to Parliament. He was replaced as Council Leader by Brian Walker and resigned his council seat after the May local elections.

Elected on 1 February 1996 in a by-election brought about by the death of the previous MP, Labour's Derek Enright, Trickett was made PPS to Peter Mandelson after Labour was elected to power and worked in the Cabinet office and subsequently the DTI. After leaving the government at the time of Mandelson's fall from grace, Trickett was chair of the Compass pressure group.

He played a significant role in rebelling against the Iraq War and participated in demonstrations against the War in London, Wakefield and Leeds. He rebelled on a number of occasions against Tony Blair's reforms to public services. He led the demands for a recall of Parliament at the time of the Israeli attacks on the Lebanon. He led the campaign inside the Commons to amend the Companies Bill to secure public listed companies reporting on 'supply chain issues' in line with the suggestions of a range of non governmental organisations. He was a leading figure in the campaign to prevent a decision to replace the Trident[1] nuclear weapons system in 2007. He was Jon Cruddas's campaign manager during the 2007 Labour Party deputy leadership election.

Trickett had previously voted against the Blair Government's 90-day detention proposals in the Terrorism Act 2006, which had been publicly advocated by the police, and was joined by both Labour and Conservative MPs in the vote, the only time Blair was defeated in the Commons. Trickett and Cruddas voted in favour of the subsequent 28-day detention proposal, and Trickett then resigned from his position in Compass after voting in favour of the legislation despite opposition to the Bill from some members of Compass.

Trickett was appointed by the trades unions as acting Chair of the Tribune newspaper Board in 2007, but gave up this role when the paper was taken over by a private proprietor.

In June 2007 he was asked by Gordon Brown to chair the party's manifesto group on housing, a position which he declined to take up.
Following the cabinet reshuffle of 3 October 2008, Trickett became the Parliamentary Private Secretary to the Prime Minister, Gordon Brown.[2]

In July 2016, Trickett apologised for comments on Twitter which appeared to liken an attempted coup in Turkey to attempts to oust Jeremy Corbyn. Labour MP Michael Dugher said: “As death toll rises to 90, I'm sure Jon Trickett will reflect and realise this comparison is not clever and not funny.” Trickett deleted the tweet and apologised, saying: “Okay okay. Tweet deleted and withdrawn. Shouldn't tweet when feeling ill. I apologise sincerely”.[10]